setsockopt: sanitize PF_PACKET SOL_PACKET options for zero-copy rings

In SOL_PACKET, we can sanitize the setsockopt() syscall a bit in the
following ways:

i) PACKET_VERSION is always checked in the kernel and it is quite
   likely to return -EINVAL here, very unlikely to crash this option.
   However, if we pass the correct values to it (TPACKET_V1, TPACKET_V2,
   TPACKET_V3), we can jump into this version specific code on other
   syscalls on that socket.

ii) PACKET_{R,T}X_RING never gets a structure of size int, so it might
    always return -EINVAL here. Depending on the TPACKET version, it
    can either be tpacket_req or tpacket_req3. Make it more likely to
    have size tpacket_req though.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>